It is increasingly common to share and exchange digital data using removable memory storage devices, which are referred to typically as “memory keys,” “memory sticks,” “flash drives,” or “thumb drives.” In general, this type of storage device is a NAND-type flash memory data storage device integrated with a USB (universal serial bus) interface. USB flash drives are typically removable and rewritable, and are supported by a wide range of portable and fixed electronic devices such as laptops, personal data analysers (PDAs), personal computers, etc. They are more compact, faster, hold much more data, have a more durable design, and are more reliable for lack of moving parts than previous removable media such as floppy discs, CD-ROM, and DVD-ROM. Storage capacities currently range from 512 MB to 32 GB, with steady improvements in size and price per gigabyte. Some allow 1 million write or erase cycles, have 10-year data retention, and are connected by USB 1.1 or USB 2.0 standard interfaces. Additionally, these types of storage devices use the USB mass storage standard supported natively by modern operating systems such as Windows, Mac OS X, Linux, and other Unix-like systems. Furthermore, their portability and optional embedding of biometric sensors and/or other authentication transducers for authenticating a user, coupled with an embedded processor for executing firmware, have made USB flash drives a common storage device for storing digital data, such as for instance digital documents, forms, applications, etc.
Of course, it is common to require some form of user authentication when private or sensitive data are stored on a USB flash drive. For instance, the user is required to provide authentication data in the form of a password or a biometric input after the USB flash drive is connected to a computer system or other electronic device. Once authenticated successfully, the user is able to read and write data from and to the USB flash drive. If the user is not authenticated successfully, then user access to the data that is stored on the USB flash drive is denied. Optionally, the USB flash drive is locked or otherwise disabled subsequent to registering a predetermined number of failed authentication attempts.
Unfortunately, even when a user is authenticated successfully, there are certain risks associated with the use of a USB flash drive for sharing digital data. For instance, the user may provide authentication data in order to allow access, by another user, to the data that is stored within the USB flash drive. Typically, this situation occurs when a manager, the first user, wishes to allow an employee, the second user, to have access to the data that is stored within the USB flash drive. In this case, the second user is trusted to use the data that is stored within the USB flash drive for a specific purpose. However, the second employee may either inadvertently or with malicious intent over-write the data that is stored within the USB flash drive, or write additional data to the USB flash drive. The first user cannot prevent the unauthorized storage of data within the USB flash drive, since the first user has relinquished control of the USB flash drive to the second user subsequent to providing the necessary authentication data. Clearly, it is impractical to require the first user to constantly oversee the usage of all USB flash drives that are authenticated in this manner.
Accordingly, there is a need for a method and system that overcomes at least some of the above-mentioned limitations of the prior art.